An in vitro investigation of the toxicity of layered silicate nanomaterials

Layered silicate nanomaterials (NMs) are a diverse group of clay minerals that have attracted great interest in various branches of industry. However, despite growing demand for these class of NMs their impact on human health has not been yet fully investigated. Therefore, the aim of this study was to evaluate the potential toxic effects of a panel of different types of synthetic and natural layered silicate NMs, of varying physicochemical properties, compared to a positive control of DQ12 quartz particles. Mouse BALB/c monocyte macrophage (J774A.1) and human peripheral blood mononuclear cells (PBMC) were chosen as in vitro models of alveolar macrophages. Based on the cytotoxicity data in J774A.1 cells, tested layered silicate NMs were grouped into: no measurable toxicity samples comprising No F/Low Li and No F/V low Li; relatively low toxicity samples consisting of No F/Med Li, High F/Med Li and High F/Med Li washed particles; intermediate toxicity samples consisting of Low F/Med Li, sHca-1and DQ12; and relatively high toxicity samples comprising Na-F-Hectorite, Med F/High Li and MMT particles. Tumor necrosis alpha (TNF-α) secretion and induction of pro-inflammatory genes indicated that Na-F-Hectorite, MMT, sHca-1, Med F/High Li and Low F/Med Li samples induced potent inflammatory responses at sub-lethal concentrations, and in many cases exceeding the effect of DQ12. Med F/High Li, Low F/Med Li, Na-F-Hectorite, MMT and sHca-1 samples induced small yet significant reactive oxygen species (ROS) production in J774A.1. However, in acellular conditions none of the tested samples increased oxidising species production, indicating a lack of their intrinsic ability to produce ROS. PBMC cells were less sensitive to tested particles and based on the cytotoxicity results tested particles were divided into non-toxic samples: No F/Med Li, High F/Med Li, High F/Med Li washed, No F/Low Li and No F/V low Li; intermediate toxicity samples consisting of DQ12, sHca-1 and Low F/Med Li; and relative high toxicity samples comprising Na-F-Hectorite, MMT and Med F/High Li. Na-F-Hectorite, MMT and sHca 1 induced secretion of TNF-α and interleukin 8 (IL-8), whereas samples of Med F/High Li and High F/Med Li were shown to enhance TNF-α secretion in PBMC. J774A.1 and PBMC cells were shown to effectively uptake No F/Med Li and sHca-1 particles. In both types of cells all the tested layered silicate NMs caused extensive cytoplasmic vacuolisation that was not mediated by mechanisms of cell death such as methuosis or paraptosis. Based on the results obtained in this study the toxic potency of tested samples appeared to be dependent on particles size with the platelets of larger dimension and lower surface area being more potent than the smaller platelet with higher surface area. In addition, there was no relationship observed between lithium and fluoride content in layered silicate particles and their impact on overall toxicity. Obtained results demonstrated that layered silicate NMs have different toxicological profiles and suggest that toxicological properties of a specific layered silicate NM should be investigated on an individual basis